McKinley P A, Smith J L
Department of Kinesiology, UCLA 90024.
J Neurosci. 1990 May;10(5):1429-43. doi: 10.1523/JNEUROSCI.10-05-01429.1990.
The organization of primary somatosensory cortex was examined in chronic spinal cats that had sustained cord transection at T12 at 3 ages: 2 and 6 weeks of age, and as adults. Five months to 1 yr following transection, the deprived cortex was mapped electrophysiologically (multiunit recordings). The topographical organization found at each age was compared to that present in normal adults to study effects of developmental age on the ability of the somatosensory system to adjust to changes in afferent input. Cortical responses to deprivation of somatosensory input were age dependent. In animals cord transected at 2 weeks of age, the remaining somatic afferent input excited both its normal cortical area and the area normally reserved for the hindlimb. This resulted in 2 somatotopic maps of the rostral trunk and forelimb. In contrast, in cats spinalized at 6 weeks of age, there was only 1 map for the remaining somatosensory input that was distributed across the mediolateral axis of the primary somatosensory cortex. As a result, the remaining somatosensory input was shifted medially from its normal position and was narrower with respect to the rostrocaudal area driven by light tactile input. The amount of cortex that each body region could excite was essentially the same as in normal animals. In adults, a third response was observed; regions normally devoted to forelimb and trunk appeared to be unchanged, and the region previously serving the hindlimb responded only to a limited extent, and only to tactile stimulation of the trunk. In all cases, however, some sites in the cortex could be excited by parts of the body that in normal animals were served by cortical regions from 3 to 10 mm away, a distance much in excess of the maximum extent of reported thalamocortical overlap. We suggest that the various patterns of cortical organization observed at different ages reflect different developmental processes that are active at the time of transection. Further, we hypothesize that often, in major denervations such as spinal cord transection, a significant component of the reorganization occurs at synaptic levels below the cortex in young animals.
在3个年龄段（2周龄、6周龄及成年）时遭受T12脊髓横断的慢性脊髓猫中，研究了初级体感皮层的组织情况。横断后5个月至1年，对失传入皮层进行电生理图谱绘制（多单位记录）。将各年龄段发现的拓扑组织与正常成年猫的进行比较，以研究发育年龄对体感系统适应传入输入变化能力的影响。皮层对体感输入剥夺的反应取决于年龄。在2周龄时脊髓横断的动物中，剩余的躯体传入输入兴奋了其正常皮层区域以及通常为后肢保留的区域。这导致了 Rostral 躯干和前肢的两个体表定位图谱。相比之下，在6周龄时脊髓横断的猫中，剩余体感输入只有一个图谱，其分布在初级体感皮层的内外侧轴上。结果，剩余的体感输入从其正常位置向内侧移位，并且相对于由轻触觉输入驱动的前后尾区域变窄。每个身体区域能够兴奋的皮层量与正常动物基本相同。在成年动物中，观察到了第三种反应；通常用于前肢和躯干的区域似乎没有变化，而先前用于后肢的区域仅在有限程度上有反应，并且仅对躯干的触觉刺激有反应。然而，在所有情况下，皮层中的一些位点可以被正常动物中由距离3至10毫米的皮层区域服务的身体部位所兴奋，这一距离远远超过了报道的丘脑皮层重叠的最大范围。我们认为，在不同年龄观察到的各种皮层组织模式反映了横断时活跃的不同发育过程。此外，我们假设，在诸如脊髓横断这样的主要去神经支配中，在幼小动物中，重组的一个重要组成部分发生在皮层以下的突触水平。
